JPH01235144A - Controlling of electron beam quantity - Google Patents

Abstract

PURPOSE:To easily follow the change when the electron beam quantity set for an object to be radiated is changed by calculating the quantity of the electron beam permeating a metal foil and changing the electric power fed into a vacuum container from a high-frequency power source. CONSTITUTION:When the electric power is fed into a vacuum container from a high-frequency power source 11 to generate plasma, it collides with a cathode to generate secondary electrons. The cathode current Ic is the sum of the ion current and the secondary electron current, this current Ic is inputted to an arithmetic unit 15. Emitted secondary electrons permeate a metal foil hermetically closing the opening section of the vacuum container, the quantity of the electron beam permeating the metal foil when the electron beam is radiated to an object to be radiated arranged on the outside of the metal foil is calculated based on the current value flowing into the cathode from a high-voltage power source applying the more negative potential than the container to the cathode, the electric power fed into the vacuum container from the high-frequency power source is changed until this calculated value becomes equal to the electron beam quantity set for the radiated object. When the electron beam quantity set for the radiated object is changed, the change can be easily followed.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention generates plasma by applying a high-frequency electric field to plasma raw material scum introduced into a vacuum container having an opening that is hermetically closed with metal foil. The generated ions in the plasma collide with a cathode arranged in the vacuum container and charged with a negative potential from the container to emit secondary electrons, and the emitted secondary electrons are transferred to the container. Electron beam irradiation, in which a metal foil that airtightly closes the opening of the vacuum container is advanced and retreated by acceleration due to a potential difference between the cathode and the object to be irradiated placed on the outer surface of the metal foil is irradiated with an electron beam. The present invention relates to an apparatus, and particularly to a method of controlling the amount of electron beam that passes through a metal foil when irradiating an object with an electron beam.

[Conventional technology]

FIG. 2 is a schematic cross-sectional view showing an example of the configuration of the main electron beam components, which are the main parts of a conventional electron beam irradiation device.

The space inside a cylindrical metal vacuum container 1, which is hermetically closed by a metal foil 4 on one open end side, is separated into upper and lower parts by a grid and a grid 3 which are at the same potential as the container, and the separated lower part An inert gas such as He or Ar is introduced into the space from a gas introduction pipe (not shown), and is turned into plasma by a high-side electric field introduced from a high frequency power source 1 through an introduction terminal 5. On the other hand, in the upper part of the separated space, a high voltage power supply 12 connects the vacuum container 1, which is at ground potential, to
A cathode 2 charged with a negative potential of about 0 kV is disposed, so that ions in the plasma f6 generated in the space below are electrostatically accelerated toward the cathode 2 charged with a negative potential, The ion beam 7 collides with the cathode 2, causing secondary electrons to be emitted from the cathode. The emitted secondary electrons are accelerated toward the ion beam 3 due to the potential difference of 200 kV between the cathode 2 and the ion beam 8.
Then, it passes through the holes 3 and 3, and further crosses the plasma 6 to reach the metal foil 4.

The metal foil 4 is, for example, a Ti film with a thickness of several tens of microns, and is thick enough to maintain a vacuum, but a part of the electron beam accelerated to 200 kV passes through this foil and enters the atmosphere. It is released and irradiates objects in the atmosphere. In the figure, reference numerals 9 and 10 indicate electrodes according to the present inventor's invention (pending application, application number unknown), both of which are formed as flat electrodes, with a grid, a dowel, and a cathode, respectively. It is placed in front of the metal foil to correct the curvature of the equipotential surface between the cathode and the electrodes, and also plays the role of applying an appropriate potential to allow the secondary electrons to efficiently reach the metal foil. Irradiation electron beam 1 that passes through the metal foil and irradiates the object to be irradiated.
Conventionally, the amount of 3 was placed outside the vacuum vessel for each set value of the negative high potential supplied to the cathode 2 from the high voltage power supply 12 and the input power input into the plasma from the high frequency power supply 1. Confirmation was very time-consuming because it was confirmed using a photosensitive material.

[Problem to be solved by the invention]

In view of the above-mentioned conventional problems, the present invention has been developed to confirm the amount of electron beam that passes through the metal foil and goes to the object to be irradiated during electron beam irradiation, and to adjust the amount of electron beam to the object that is set in advance for the object to be irradiated. It is an object of the present invention to provide a method for controlling an electron beam generating unit so that the electron beam is automatically equal to , and to realize a control method that can easily follow the electron beam dose set to the irradiated object even if it changes. This should be an important issue.

[Means to solve the problem]

In order to solve the above problems, according to the present invention, a high-frequency electric field is applied to a plasma raw material gas introduced into a vacuum container having an opening hermetically closed with a metal foil to generate plasma. Ions in the plasma collide with a cathode arranged in the vacuum container and charged with a negative potential from the container to emit secondary electrons, and the emitted secondary electrons are transferred between the container and the cathode. The electron beam passes through a metal foil that airtightly closes the opening of the vacuum container by being accelerated by the potential difference of A method for automatically controlling the amount of electron beam is to calculate the amount of electron beam passing through the metal foil using the current value flowing into the cathode from a high voltage power source that applies a negative potential to the cathode from a container. The method is such that the electric power input from the high frequency power source for converting the raw material gas into plasma is changed into the vacuum vessel until this calculated value becomes equal to the electron beam dose set for the object to be irradiated.

[Effect]

This method configures an electron beam that is irradiated onto an object.

There is a certain condition between the amount of secondary electrons emitted from the cathode 2 and the cathode current flowing into the cathode 2 from the high voltage power supply 12, which is determined by the configuration of the electron beam generating section and its operating conditions. This study focuses on the possibility of controlling the irradiation electron dose by utilizing this cathode current, and is developed as follows. That is, first, the secondary electron emission value γ of the cathode 2, that is, the ratio of the electron current 1e due to the emitted electrons to the ion current 1i formed by the colliding ions is measured and inputted into the function generator. Since this secondary electron emission sr depends on the constituent material of the cathode 2, the ion species, and its manufacturer, the emission rate is measured for each combination of these factors, and the configuration of the electron beam generating section and its operation are measured. input so that the value corresponding to the condition is obtained as the output. Therefore, if the current flowing into the cathode from the high voltage power supply 12 is Ic.

This Ic is the sum of the ionic current 1i flowing into the cathode 2 and the electron current 1e, and since Ie=yIi, Ic
=Ii-)1e=÷Ie+Ie=(Eng+l)
From Ie and Nari, the secondary electron current is Ie = +
It is found as Ic. This secondary electron current 1e is attenuated by scattering from the time it leaves the cathode 2 as an electron beam 8 until it passes through the metal foil 4, and the aperture ratio of the electrodes 9, 10 and the grid 3 (progress of the electron beam 8) is attenuated by scattering. Let the ratio of the projection surface area through which the beam can pass to the total projected area of the electrodes on a plane perpendicular to the direction be P, , P2 and PS, respectively, and the transmittance of the plasma 6 and the metal foil 4 be P, , P, respectively. For example, the irradiation electron dose transmitted through the metal foil 4 is 1 rad i
i Irad=Ie op, *P2 aP3 op4
*P5 = T tenth 1cm PH-P2 spa a
It becomes P4 * PS. Here, P1 to P3 are constants determined from the shape and dimensions of each electrode, so P, xP2x
It operates by setting P3 = α (constant). Regarding P4, the relationship between the plasma density, which has a correlation with the input power from the high-frequency power source 11, and 2 trillion rugi of electrons, and regarding Ps, the relationship between the constituent material of the metal foil 4, its thickness, and the 2 trillion rugi of electrons. The transmittance p4. was actually measured and corresponded to each of these factors. p.

is input to the function generator so that it is output.

In this way, based on the configuration of the electron beam generator and its operating conditions, the corresponding values of r and αg P4 + PS are output from the function generator, and these outputs are combined with the cathode current Ic. By combining, the amount of electron beam transmitted through the metal foil is Irad=+*Ic 1
1 a * P4 * PS. Therefore, by comparing this electron dose with a preset amount for the irradiated object and changing the power input from the high-frequency power source into the plasma until the two become equal, irradiation with the predetermined electron dose is automatically performed. Furthermore, even if the electron beam dose set for the object to be irradiated changes, it can be easily followed.

〔Example〕

Figure 1 shows a practical example of the present invention. First, a high frequency power source 1
] When electricity is input into the vacuum chamber to generate plasma, the ions in the plasma are accelerated toward the cathode,
It collides with the cathode and generates secondary electrons. A current flowing into the cathode from the high-voltage power supply 12, that is, a cathode current Ic, is the sum of an ion current and a secondary electron current, and this current 1c is input to the calculator 15. On the other hand, the tooth electrode material and ionic species of the electron beam generating section.

Since the acceleration energy given to the ion species from the high voltage power supply 12 is given by the configuration of the electron beam generation section and its operating conditions, these are input to the function generator 14 to calculate and output the secondary electron emission sr. let

Furthermore, since the input power from the high frequency power source 11 that provides plasma density and the acceleration energy from the high voltage power source 12 that accelerates secondary electrons are also given from the operating conditions of the electron beam generator, these are input to the function generator 14. to output the plasma transmittance P4 of secondary electrons.

Furthermore, since the constituent material and thickness of the metal foil are also given by the configuration of the electron beam generator, these are input to the function generator 14,
In combination with the previously input secondary electron acceleration energy, the secondary electron metal foil transmittance P is output. Also, the second
Since α obtained from the aperture ratio of each of the electrodes 9 and 10 and the grid and gate 3 in the figure is a constant specific to the main component of the electron beam,
These α.

p4. Input p, , γ into the calculator 15, and combine with the previously input Ic to calculate the electron dose 1 r that passes through the metal foil.
ad is calculated, the difference from the preset electron dose for the irradiated object is found, and this difference is used to change the input power from the high frequency power source until this difference becomes zero, that is, the control input becomes zero. Change input power.

〔Effect of the invention〕

As described above, according to the present invention, once the configuration of the electron beam generating section and its operating conditions are determined, the cathode current flows from the high voltage power supply to the cathode and passes through the metal foil to the irradiated object. Since the amount of electron beam can be determined, the effort of checking the electron beam amount for each operating condition is saved1, and even if the electron dose set for the irradiated object changes, it can be easily followed and transmitted. Since the electron dose is controlled, it is also possible to automatically set the electron dose to the irradiated object.

[Brief explanation of the drawing]

FIG. 1 is a functional diagram showing an example of an uninvented electron dose control method, and FIG. 2 is a schematic sectional view showing an example of the configuration of an electron beam generating section in an electron beam irradiation apparatus. 1... Vacuum container, 2... Cathode, 4... Metal foil, 6
... Plasma, 7... Ion beam, 8... Electron beam, 1]... High frequency power supply, 12... High voltage power supply, 13... Irradiated electrons Figure 1

Claims (1)

[Claims] 1) Plasma is generated by applying a high-frequency electric field to a plasma raw material gas introduced into a vacuum container equipped with an opening that is hermetically closed with metal foil, and ions in this plasma are arranged in the vacuum container. The container collides with a cathode charged with a negative potential to emit secondary electrons, and the emitted secondary electrons are accelerated by the potential difference between the container and the cathode to open the opening of the vacuum container. A method for transmitting an electron beam through a metal foil that airtightly closes the metal foil, and controlling the amount of an electron beam that passes through the metal foil when irradiating an object to be irradiated placed outside the metal foil with the electron beam, The amount of electron beam transmitted through the metal foil is calculated using the current value flowing into the cathode from a high voltage power source that applies a negative potential to the cathode from the container, and this calculated value is set for the irradiated object. 1. A method for controlling an electron dose, comprising changing the electric power input into a vacuum container from a high-frequency power source for converting the source gas into plasma until it becomes equal to the electron dose applied to the source gas.